The leader of one of Africa's poorest and least-known countries has appealed for help from France and the US as rebel soldiers continue their advance toward the capital.

Rebels have already taken control of the Central African Republic's third largest city Bambari, and the diamond-rich area of Bria.

Now, president Francois Bozize - who himself seized power in a coup in 2003 - has appealed for international help to block rebels from the capital Bangui.

"We ask our French cousins and the United States of America, the great powers, to help us to push back the rebels... to allow for dialogue in Libreville to resolve the current crisis," Mr Bozize told supporters at a rally in Bangui.

"There is no question of allowing them to kill Central Africans, of letting them destroy houses and pillage, and holding a knife to our throats to demand dialogue.

"It is a plot against the Central African Republic, a plot against its people."

But former colonial power France, whose embassy in Bangui came under attack earlier this week by demonstrators angry at the lack of help from Paris, has vowed it will not intervene in the country.

This morning the United States said it was evacuating its embassy in the country and temporarily halting its operations amid security fears.

The US State Department said it had not broken off diplomatic ties with the country's beleaguered government, but warned US citizens not to travel to the mineral-rich but chronically unstable country.

The United Nations has already begun evacuating non-essential staff and described the mood in the country as tense.

Journalist Hippolyte Marboua, who is in Bangui, says people are stockpiling food amid fears the rebels may try to enter the city in the coming days.

"My impression is that the government is no longer in a position to guarantee the security of the country," he said.

"The rebels are advancing and there's no resistance from the Central African armed forces.

"Meanwhile staff from NGOs and other international organisations have already started being evacuated."

The Central African Republic has been coup-free for the past few years, but it is a nation with a turbulent history.

One of its most infamous coup leaders, former president Jean-Bedel Bokassa, was sentenced to death in absentia for crimes against humanity, including cannibalism.